Hydraulic forming press



July 16, 1968 H. MOLLER HYDRAULIC FORMING PRESS Filed May 25, 19653,392,563 HYDRAULIC FORMING PRESS Hugo Miiller, Trollhattan, Sweden,assignor to Saab Aktiebolag, Linlroping, Sweden, a corporation of SwedenFiled May 25, 1965, Ser. No. 458,672 Claims priority, applicationSweden, May 29, 1964, 6,530/64 1 Claim (Cl. 72-63) ABSTRACT OF THEDISCLOSURE In a hydraulic forming press for sheet metal blanks having apressure chamber body with a bore therethrough that is closed near itsbottom by a resilient cup-shaped diaphragm and having a forming toolbeneath the diaphragm which is adapted to enter the bore, a ring closelysurrounds a reduced diameter lower portion of the diaphragm. The ringhas a coplanar bottom surface engageable with an upwardly facing surfaceon the forming tool. The ring accommodates radial play of the formingtool relative to the bore in the body and prevents intrusion of thediaphragm into the space between the forming tool and the pressurechamber body.

This invention relates to hydraulic presses for forming sheet metalblanks, and refers more particularly to hydraulic forming presses of thetype comprising a pressure chamber body with a vertical boretherethrough that is closed near its bottom by a resilient cup-shapeddiaphragm, and a forming tool beneath the diaphragm which is adapted toenter the bore and against which a sheet metal blank can be forminglypressed by pressure fluid confined in the bore above the diaphragm andexerting force through the diaphragm.

In hydraulic presses of the character described the forming tool usuallycomprises a central punch which is fixed on the press table and has anupwardly projecting forming portion, and a blank holding ring whichencircles the punch and has a flat upper surface. The pressure chamberbody, in the bore of which a resilient cupshaped diaphragm is so securedas to be confined against bodily axial motion, is movable upwardly anddownwardly relative to the punch and the clamping ring.

When a sheet metal blank is to be formed, it is placed on the clampingring, and the pressure chamber body is lowered to cause the marginaledge portion of the blank to be clampingly confined between thediaphragm and the clamping ring. While maintaining clamping force uponthe marginal portion of the blank, the pressure chamber body continuesto descend in unison with the clamping ring, and as the fixed punchupwardly displaces the central portions of the blank and diaphragm,fluid under pressure in the pressure chamber body, acting through thediaphragm, acts upon the blank to form it to the shape of the formingtool.

In order to obtain clamping relationship between the diaphragm and theblank holding ring of the forming tool, the blank holding ring mustenter the lower portion of the bore in the pressure chamber body as thelatter moves down. This requires that there be a certain clearancebetween the forming tool and the bore surface in order to insure thatthey do not bind, and such clearance must be great enough to allow forvariations in working temperature of the parts.

Heretofore the useful life of the cup-shaped diaphragm in such a presshas depended upon the closeness of fit between the forming tool and thebore in the pressure chamber body, because the diaphragm, under the highpressures to which it is subjected in forming operations of this type,becomes almost plastic, and the material nited States Patent of thediaphragm therefore tended to penetrate into any space that existedbetween the blank holding ring and the bore surface of the pressurechamber body, with the result that the diaphragm was more or lessgradually crumbled. In order to prolong the useful life of the cupshapeddiaphragm, which is relatively expensive, the prior practice has been tomachine the forming tool and the bore in the pressure chamber body tofit one another as closely as possible. The accurate machining of theseparts was relatively expensive, and to some extent economy in diaphragmlife was achieved at the sacrifice of economy in machining the bore andforming tool. But even close machining could not overcome the problemcreated by changes in temperature of the parts. Furthermore, when theforming tool and pressure chamber body bore were made to fit one anotherwith very small clear ance, extreme care was required in assembling theforming tool on the press to insure that it was accurately centered withrespect to the bore. In view of these difiiculties, it was not possiblein practice to achieve such an accurate fit between the forming tool andthe bore in the pressure chamber body as to obtain a satisfactorily longuseful life of the diaphragm.

With the foregoing considerations in mind, it is a general object ofthis invention to provide means in a hydraulic forming press of thecharacter described for providing its cup-shaped resilient diaphragmwith a satisfactorily long useful life while at the same time obviatingthe need for obtaining a close and precise fit between the forming tooland the bore in the pressure chamber body.

Thus it is a general object of this invention to achieve substantialeconomies in the operation of a hydraulic press of the characterdescribed by prolonging the useful life of its diaphragm and by alsoreducing the cost of machining the forming tool and pressure chamberbody.

Another object of the present invention is to simplify the mounting ofthe pressure chamber body and forming tool in a hydraulic press of thecharacter described, while at the same time prolonging the useful lifeof the diaphragm, by the provision of inexpensive means that makespossible a comparatively loose fit of the forming tool in the bore ofthe pressure chamber body, so that the tool and body need not beaccurately centered relative to one another, such loose fit alsoeliminating the risk that the tool and body will bind in one another andthereby assuring safe functioning of the press.

A further and more specific object of this invention is to achievesubstantially reduced costs in the operation of a hydraulic formingpress by the provision of a simple, inexpensive and easily replaced ringwhich encircles the lower portion of the cup-shaped diaphragm in such apress and projects a small distance below the diaphragm, said ring beingaxially displaceable to some extent but being retained against bodilyaxial displacement out of the bore in the pressure chamber body bycooperating means on the ring and on said body, and said ring having abottom surface which can engage the top surface of the forming tool witha close fit to accommodate play between the forming tool and thepressure chamber body while also preventing the diaphragm from intrudinginto the clearance space between them.

With the above and other objects in view which will appear as thedescription proceeds, this invention resides in the novel construction,combination and arrangement of parts substantially as hereinafterdescribed and more particularly defined by the appended claims, it beingunderstood that such changes in the precise embodiment of thehereindisclosed invention may be made as come within the scope of theclaims.

The accompanying drawing illustrates one complete example of thephysical embodiment of the invention constructed according to the bestmode so far devised for the practical application of the principlesthereof, and in which:

FIGURE 1 is a fragmentary view, partly in side elevation and partly invertical section, of a hydraulic forming press embodying the presentinvention; and

FIGURE 2 is a fragmentary vertical sectional view on an enlarged scaleof a portion of the press structure shown in FIGURE 1.

Referring now to the accompanying drawing, the numeral 5 designatesgenerally the working portion of a hydraulic press, comprising amounting plate 6 which is adapted to be fastened to a press head, apressure chamber body 7 which is suspended from the mounting plate 6 forrelative up and down motion and which has a vertical bore 8therethrough, a cup-shaped diaphragm 9 which is secured in the lowerportion of the bore 8, and a forming tool 10 which is carried by a presstable 11 beneath the pressure chamber body 7.

The pressure chamber body 7 is mounted for up and down motion relativeto the plate 6 by means of a plurality of long bolts 12 which have theirheads lowermost and which extend upwardly through holes in radiallyoutwardly projecting flange means 13 on the pressure chamber body, nearthe top thereof, and have their threaded upper end portions engaged invertically aligned threaded holes in the plate 6 and secured by locknuts 14. A helical compression spring 15 is confined between the head ofeach bolt and the flange means 13 thereabove, to provide yieldingsupport for the pressure chamber body.

The cup-shaped resilient diaphragm 9 is secured in the bore 8 in thepressure chamber body, with its bottom spaced a small distance above thelower end of the bore and with its circumferential side wall 16projecting upwardly and providing a seal around the bore. To confine thediaphragm against bodily axial motion relative to the pressure chamberbody, the side wall of the diaphragm is formed with a radially outwardlyprojecting circumferential land 17 which is received in a mating groove18 that extends around the bore. An expansion ring 19 inside thediaphragm side wall, radially opposite the land 17, maintains the landengaged in the groove 18 during operation of the press but is readilyremovable to provide for replacement of the diaphragm. The bottom wall20 of the diaphragm has substantially flat, parallel top and bottomsurfaces, and, although illustrated as being of unitary construction, itcan be formed in three parts, for purposes of replacement economy, inaccordance with the principles of the invention disclosed in thecopending application of Hugo Moller, Ser. No. 458,673, filed May 25,1965 and now Patent No. 3,334,504.

Cooperating with the diaphragm to define a pressure fluid chamber in thebody 7 is a plunger 22 which is slidably received in the upper portionof the bore 8 and which has a spherically concave undersurface 23. As isconventional, the plunger is removably mounted on the press head (bymeans not shown) for up and down motion in the bore, by which fluidtherebeneath can be placed under pressure. A venting duct 24, closed bya screw 25, extends through the plunger for bleeding air out of thepressure chamber as the same is filled with hydraulic fluid.

The plunger has a reduced diameter bottom portion which provides acircumferential recess in which there is received a resilient sealingring 26 of U-shaped crosssection with its legs projecting downwardly. Arigid retaining ring or washer 27, secured to the underside of theplunger by means of screws 28, engages under the radially inner leg ofthe sealing ring to confine the sealing ring against axial displacementrelative to the plunger. The sealing ring is so arranged that itsradially outer leg engages the bore surface and is forced more snuglyagainst the same as pressure is increased on the fluid beneath theplunger.

The forming tool 10 comprises a rigid stationary punch 29 which isattached to the stationary press table 11 and a blank holding ring 30which encircles the punch. The blank holding ring has a flat uppersurface and is mounted for up and down motion on pressure rods 31 thatextend through guide holes 32 in the press table and are adapted to beacted upon by force exerting means (not shown) in such a manner that theblank holding ring can descend with the pressure chamber body whileyieldingly resisting downward motion so as to react upwardly against thediphragm and cooperate with it in imposing clamping force upon themarginal edge portion of a sheet metal blank 33. As the pressure chamberbody and blank holding ring descend, the central portion of the diphragmis displaced upwardly by the punch, and the force of pressure fluid inthe pressure chamber, transmitted through the diaphragm, forces theblank into a shape conforming to that of the forming tool.

Although the forming tool comprising the blank holding ring 30 and punch29 enters the lower portion of the bore 8 in the pressure chamber bodyduring each forming operation of the press, it is a feature of thisinvention that the blank holding ring need not fit closely in the boreand, in fact, preferably fits it with a substantial clearance.Nevertheless the diaphragm is prevented from intruding into thisclearance space by reason of the provision of a substantially rigidsealing ring 34 which encircles the lower portion of the diaphragm andprojects a small distance beneath the same.

The sealing ring 34 is retained in the bore by c0- operating retainingmeans on the ring and on the pressure chamber body, comprising aradially outwardly projecting circumferential land 35 on the sealingring, defining a downwardly facing shoulder, and a land 36 on thepressure chamber body, projecting radially into the bore and extendingcircumferentially therearOund at a distance above the bottom of the boreto provide an upwardly facing shoulder which engages the downwardlyfacing shoulder on the sealing ring. To provide the land 35 on thesealing ring, the sealing ring can have a stepwise reduced outsidediameter, its upper portion being larger in outside diameter than itsmain body portion. To provide space for the sealing ring between thepressure chamber body and the diaphragm, the diaphragm has a reducedoutside diameter at its bottom portion that defines a notch or recess 37in which the sealing ring has a substantially close fit.

The sealing ring 34 has a fiat coplanar bottom surface which cooperateswith the flat upper surface on the blank holding ring, and since thesealing ring projects a distance below the bottom of the diaphragm andis free for a certain amount of axial movement to and from the positionin which its land 35 engages the land 36 on the pressure chamber body,pressure applied to the diaphragm forces the sealing ring into intimateengagement with the top surface of the blank holding ring when the pressis closed. As a result, the sealing ring 34 of this invention serves tobridge any radial play between the forming tool and the surface of thebore 8, while preventing the diaphragm from intruding into the radialspace between them. Hence the forming tool can be made to fit the borewith a substantially loose fit and without the need for accuratelymaintained tolerances. It will be apparent that the sealing ring thuseliminates the need for special precautions with respect to centeringthe forming tool relative to the bore and accommodating variations inthermal expansion of the forming tool and pressure chamber body.

Installation of the sealing ring of this invention is relatively simple.With the plunger 22 and diaphragm 9 removed from the bore 8, the sealingring 34 can be installed by merely inserting it axially into the borefrom the top thereof until the land 35 on the sealing ring engages theland 36 on the pressure chamber body, after which the diaphragm 9 issimilarly inserted into the bore 8 until its land or collar 17 engagesin the groove 18 in the pressure chamber body. The diaphragm is thensecured by the expansion ring 19.

It will be evident that the sealing ring 34 could be formed as a splitring, and that it could be retained in place by any of the severalobvious equivalents of the particular land arrangements hereinspecifically disclosed for purposes of illustration, so long as it isallowed some degree of displacement by which it can be snugly engagedwith the blank holding ring under downward force exerted by thediaphragm when the press is closed.

From the foregoing description taken together with the accompanyingdrawings it will be apparent that this invention provides simple,inexpensive and very effective means in a hydraulic forming press forprolonging the useful life of the resilient cup-shaped diaphragm in sucha press while still allowing the forming tool and pressure chamber bodybore to be formed with a substantially loose fit that facilitates andreduces the cost of machining and aligning them.

What is claimed as my invention is:

1. A hydraulic forming press of the type comprising a pressure chamberbody having a downwardly opening bore therein, a forming tool beneathsaid body a portion of which is adapted to enter the lower portion ofsaid bore, and a cup-shaped resilient diaphragm in said bore, spacedabove the lower end thereof, which closes the bore and cooperates withthe body to define a pressure chamber above the diaphragm and whichtransmits the force of pressure fluid in said chamber to a blanktherebeneath to form the blank to the shape of the forming tool, saidforming press being characterized by:

(A) the forming tool having a diameter smaller than that of said bore,to fit the bore with substantial radial clearance;

(B) the lower portion of the diaphragm having a reduced outside diametersmaller than that of the forming tool to define a downwardly facingcircumterential shoulder on the diaphragm;

(C) a sealing ring in said bore closely surrounding said reduceddiameter lower portion of the diaphragm said sealing ring (1) having atits top a circumferential flange that projects radially outwardly andunderlies said shoulder on the diaphragm, and which flange has anoutside diameter to closely fit said bore, and

(2) having a coplanar bottom surface which is engageable with acircumferential upwardly facing surface on the forming tool; and

(D) a circumferential land on the pressure chamber body projectingradially into said bore near the bottom thereof and engageable by theunderside of said flange on said sealing ring for holding the latteragainst bodily axial displacement out of the bore in the pressurechamber body so that the sealing ring can be confined between thediaphragm and the forming tool with the bottom surface of the sealingring in snug engagement with said surface on the forming tool, wherebythe sealing ring can accommodate radial play of the forming toolrelative to the surface of said bore and can provide a seal around thediaphragm which prevents intrusion of the latter into the space betweenthe forming tool and the pressure chamber body.

References Cited UNITED STATES PATENTS 5/ 1962 GrankoWski 72-63 1/ 1963Mitchell '7263

